The invention relates to an apparatus for holding and positioning a substrate cassette, particularly a wafer cassette, in wafer processing and/or inspection devices.
Substrate cassettes serve for the transport and storage of substrates such as wafers, optical flats, hard discs etc. The substrates are held in the cassettes so that the surfaces of the substrates cannot be touched either by the cassette supporting surfaces or by substrate wafers deposited adjacent to them.
Such substrate cassettes have a wide field of application in the present-day semiconductor industry. In systems which process and/or inspect such substrate wafers, care must be taken to ensure that the substrates can be removed from the substrate cassettes without any problems and that, after processing or inspection, the substrate wafers can be automatically deposited in prepared substrate cassettes again.
In order to be able to stipulate a precisely defined position of the substrate in a processing system, it must be possible to hold the substrate cassette as precisely as possible in a simple manner in such a system, and to be able to position it if necessary, in accordance with the position aimed at. That is to say the operator of an inspection device must be able to adjust a prescribed position of a cassette as quickly as possible.
Existing substrate-cassette supports have the disadvantage that they mostly do not permit any precise positioning of the substrate cassettes. In addition, particularly in the case of substrate-cassette supports which allow substrate cassettes of different sizes to be received, it is difficult and complicated to find the basic position to be assumed.
In many substrate-cassette supports it is even possible to position the substrate cassettes wrongly which, with automatic access of an inspection system to a substrate wafer in such a cassette, may possibly lead to damage to substrate wafer and/or cassette.
In addition, the stacking frames in such substrate cassettes are generally so formed that, after having been deposited in the cassette, the substrates or wafers assume a position inclined downward towards the rear wall of the cassette in an attempt to prevent them to be held from slipping forwards out of the cassette or at least to prevent their front edges projecting out of the cassette during the transport of such substrate and/or wafer cassettes. Thus the inclined position with respect to the rear wall has entirely the desired function during transport.
On the other hand, a processing system or an inspection device should be in a position to remove automatically a wafer from such a wafer cassette once it has been detected and to process or inspect it. This means that after the wafer has been successfully detected, for example by an automatic, contactless detection system, it must be possible to travel over the surface of the wafer without any problems. This involves control engineering difficulties if, for example, the handling system has to descend continuously as it travels over the wafer, or if a robot arm of such a handling system has to penetrate into the cassette in a specific angular position, which takes up an excessive amount of space.
It is an object of the present invention to provide a holding and positioning apparatus for a substrate or wafer cassette able to achieve as simple and secure a basic positioning as possible of the cassette, and which can then bring the cassette into a preselected working position to be by systematic readjustment.